IL-34 Expression in Gingival Fibroblasts, Gingival Crevicular Fluid and Gingival Tissue

Abstract: IL-34 is a protein associated with bone degenerative diseases but the role in periodontal disease is unknown. The aim of this study was to assess the expression of IL-34 in primary human gingival fibroblasts (GF) and investigate if the expression is regulated by the pro-inflammatory cytokines interleukin-1 (IL-1β) and tumor necrosis factor α(TNF-α). We also investigated if IL-34 is detectible in gingival crevicular fluid (GCF) in healthy, gingivitis and periodontitis sites. Furthermore, we examined if healthy and inflamed gingival tissue contains IL-34. GF were stimulated by IL-1β300 pg/ml and TNF-α10 ng/ml. IL-34 mRNA was measured by quantitative real-time PCR (qPCR). GCF was collected from 11 healthy, 10 gingivitis, and 21 periodontitis gingival crevices. IL-34 protein was quantified using enzyme-linked immunoabsorbent assays (ELISA). Healthy and inflamed gingival tissue biopsies were collected and examined using immunohistochemistry (IHC). IL-34 mRNA was expressed in GF and the expression was enhanced 12x fold-change versus control by TNF-α10 ng/ml and 4x fold-change versus control by IL-1β300 pg/ml. IL-34 was also present in GCF but no significant difference in IL-34 protein was detected between the healthy, gingivitis, and periodontitis groups. Healthy and inflamed gingival tissue showed equal amounts of IL-34 protein in the epithelium while sub-epithelially the inflamed tissue showed higher levels of IL-34 protein. Pro-inflammatory cytokines stimulate IL-34 mRNA expression in GF. IL-34 protein is present in GCF and gingival tissue which demands further investigation about the eventual role of IL-34 in the pathogenesis of periodontitis.